Stereoselective Chemoenzymatic Synthesis of the Four Stereoisomers of l-2-(2-Carboxycyclobutyl)glycine and Pharmacological Characterization at Human Excitatory Amino Acid Transporter Subtypes 1, 2, and 3

Abstract

The four stereoisomers of l-2-(2-carboxycyclobutyl)glycine, l-CBG-I, l-CBG-II, l-CBG-III, and l-CBG-IV, were synthesized in good yield and high enantiomeric excess, from the corresponding cis and trans-2-oxalylcyclobutanecarboxylic acids 5 and 6 using the enzymes aspartate aminotransferase (AAT) and branched chain aminotransferase (BCAT) from Escherichia coli. The four stereoisomeric compounds were evaluated as potential ligands for the human excitatory amino acid transporters, subtypes 1, 2, and 3 (EAAT1, EAAT2, and EAAT3) in the FLIPR membrane potential assay. While the one trans-stereoisomer, l-CBG-I, displayed weak substrate activity at all three transporters, EAAT1-3, we found a particular pharmacological profile for the other trans-stereoisomer, l-CBG-II, which displayed EAAT1 substrate activity and inhibitory activity at EAAT2 and EAAT3. Whereas l-CBG-III was found to be a weak inhibitor at all three EAAT subtypes, the other cis-stereoisomer l-CBG-IV was a moderately potent inhibitor with 20-30-fold preference for EAAT2/3 over EAAT1.

Synthesis of 3‐Azabicyclo[3.2.0]heptane Derivatives as γ‐Aminobutyric Acid Analogues through Intermolecular [2+2] Photo­cycloaddition

“…Therefore, N-Boc-protected 3-pyrroline was replaced by N-(trifluoroacetyl)-3-pyrroline (6). [21] Gratifyingly, these conditions also worked in the present case; with 0.10 equivalents of sensitizer the yield of the cycloaddition product 7 amounted to 39 %. [21] Gratifyingly, these conditions also worked in the present case; with 0.10 equivalents of sensitizer the yield of the cycloaddition product 7 amounted to 39 %.…”

“…First, [2+2] photocycloaddition reactions were undertaken with N-Boc-protected 3-pyrroline, [23] which was prepared from 3-pyrroline according to a literature procedure developed by Meyers et al [24] However, irradiation of mixtures of N-Boc-3-pyrroline and maleic anhydride 5 with light of a wavelength of 254 nm either in the presence or in the absence of a sensitizer (acetophenone, [21] benzophenone, [25] acetone [26] ) did not meet with any success. Therefore, N-Boc-protected 3-pyrroline was replaced by N-(trifluoroacetyl)-3-pyrroline (6).…”

4,4‐Dimethyl‐ and Diastereomeric 4‐Hydroxy‐4‐methyl‐ (2S)‐Glutamate Analogues Display Distinct Pharmacological Profiles at Ionotropic Glutamate Receptors and Excitatory Amino Acid Transporters

“…34 The scope and limitations of this enzymatic procedure have been explored extensively by us with the aim of synthesizing a large variety of Glu analogues 26. 28, 30, 33–36 With compounds 1 – 3 in hand, we first investigated them in a binding assay at native AMPA, KA, and NMDA receptors and subsequently at the cloned rat homomeric KA receptor subtypes iGluR5–7 (Table 1). The 4,4‐dimethyl‐Glu analogue 1 was shown to be a low‐affinity ligand at native AMPA, KA (the radioligand binding assay predominantly reflects binding affinities to KA1, 2‐containing subtypes), and NMDA receptors, and only displayed medium‐range nanomolar affinity for iGluR5 with a 28‐ and 7‐fold preference over iGluR6 and iGluR7, respectively.…”

Multi‐Enzymatic Cascade Reactions: Overview and Perspectives

“…In this case the amino acid racemase is of course omitted [Scheme 14 (b)]. [67][68][69] Interestingly, amino acid dehydrogenases and atransaminases have also been coupled in a linear way, realizing a system for deracemization of amino acids. [70] Branched-chain amino acid transaminase (BCAAT) from Sinorhizobium meliloti ATCC 51124 was cloned and overexpressed in E. coli.…”